Ebonising Basics
by the Hermit
Introduction
Many of us have an aversion to commercial stains and dyes, yet would sometimes like to darken or blacken a piece of timber. The answer is ebonising, a traditional method of darkening timbers that are high in tannic acid¹ , such as Walnut or Oak, by the use of vinegar and iron in the form of steel wool.
This process also works well with a range other timber types, including many if not all Eucalypts. Red Gum, Jarrah and Blackbutt work particularly well.
¹Tannic acid is not tannins, as found in tea, so don't waste your time...
(Tannins in solution will produce tannic acid, but I believe that in tea it is in such a low concentration that it's useless.)
I’ve found that there are two approaches to ebonising - the first more common (and easiest/fastest) method is to dissolve steel wool in vinegar to produce an ebonising solution in which the timber to be blackened can be soaked. Alternatively, the solution can be brushed on coat by coat, for more controllable but slightly lighter results.
The second method is to rust away the steel wool using salty water, then reduce the mixture and remove the salt, resulting in a fine black ferric oxide powder, similar to carbon black. This powder is wetted with vinegar to produce a fine paste then rubbed into timbers that don’t darken by the solution method, to produce a matt black finish. The powder remains ‘loose’, so a fixative is needed to cement the ferric oxide particles in place. I used this system on dowel with wipe-on polyurethane as a fixative with good results.
This is not truly ebonising and is really only a work-around for timbers that won’t ebonise by the usual method. It works best on small areas and parts and may appear uneven on larger surfaces.
Ebonising Solution
All that’s needed is some #0000 steel wool, (even supermarket steel wool will work, but first boil it or wash well with detergent to remove any soap or oils for best results), and a bottle of white vinegar.
I used 50g of steel wool with 2 litres of vinegar, to produce a strong solution that can be diluted 2:1 to 5:1 with vinegar before use.
First, pull the steel wool apart, shredding as much as possible,
When soaking the steel wool, air is essential, or the steel wool will take ages to begin to rust. A shallow, flat-bottomed container is fastest, with a thin layer of vinegar across the bottom, covering the bottom quarter or so of the steel wool. Don't put the whole lot of the vinegar in at once.
This way, you get visible rust within the hour.
It takes several days to dissolve the steel wool. Each time the reaction slows, I pour off the fluid into a jar and pour fresh vinegar in until I’ve used all 2 litres.
Turning the steel wool over every now and then helps, too.
The result is a brownish liquid, with the ferric oxide particles in suspension. (Always shake before use.)
The degree of darkening is dependent on the amount of tannic acid in the timber and the amount of time that the timber is left soaking. Some trial and error on scraps is recommended.
For a full black shade, I leave the timber soaking for 6 hours, to ensure maximum penetration.
Often, the timber will look dark greyish when dry after ebonising, but will blacken further when a finish is applied.
After the ebonising is finished and the required shade has been achieved, it’s a good idea to soak the timber in a sodium bicarbonate solution for a while, then rinse well with tap water. This will neutralise the acidity of the vinegar and prevent possible future cracking.
If the timber is soaked for a long enough period, ebonising will penetrate a little deeper than conventional stains and dyes and allows light sanding without going through the surface. Like stains, penetration is deepest in the end-grain.
It’s a good idea to sand the item well before ebonising, to minimise the effect of grain-raising when the timber is wetted, then only very light sanding is needed afterwards.
This solution darkens skin almost as well as it does timber and takes forever to wear off, so be sure to wear rubber gloves while handling it. Plenty of newspaper to avoid splashes is a good idea, too.
I’ve found that the solution can be re-used a number of times. I keep the partly-used solution separate, use it a few times, then discard it when it seems to be losing strength.
Here are a few samples of commonly used timbers after ebonising: -
Ebonising Powder
The other method of making eboniser that I tried involved first rusting the steel wool with salty water, then reducing the mix to a black powder while removing the salt by heating to keep the salt dissolved, allowing the mix to settle, then decanting off the liquid, evaporating the last bit and crushing the result into a fine powder. The powder is then added to vinegar as needed, to produce either an ebonising solution as above, or a fine paste for rubbing into timbers that won’t ebonise by the usual process.
To start the process, I salted the steel wool well, then poured in boiling water to partly cover the steel wool, then regularly added water as it evaporated. Once the steel wool had rusted away, I transferred the mix onto the stove, at about 60°C for settling and pouring off the salty water.
As mentioned earlier, the paste method requires a follow-up coat of polyurethane or similar as a fixative.
Like the solution, ebonising powder will stain your hands, so wear gloves.
If you have any questions, or if I’ve forgotten something, or made a mistake, please let me know.
Special thanks to fellow member and model-maker extraordinaire, j&j.
Thanks, Jim, for putting me onto ebonising in the first place and passing on the method of making the solution.
Edit: For timbers that are low in tannic acid and won't ebonise successfully, the tannic acid level in the timber can be raised prior to application of the ebonising solution, either chemically by the addition of a dilute tannic acid mixture, or by soaking (Paraguyan) ²Quebracho bark in water, then applying the solution to the timber. Another soaking in the Quebracho bark tea is also recommended after ebonising, to fully bring out the black. I have not tried these methods, but they are reputed to work well. I'd be most interested in hearing the results from anyone who tries this. I might at some later time myself.
²Quebracho bark is used in the taxidermy process and is apparently available from taxidermist suppliers. A heaped tablespoon mixed well into a pint of hot water is the recommended dilution rate.
